Cloned Animals Suffer From Obesity

After the news that Dolly the sheep has arthritis and that cloned mice may have a reduced life-span, Nature Medicine (Vol. 8, No. 3, March 2002, p. 262) reports on a further abnormality of animals produced using the technique: cloned mice are also prone to adult-onset obesity.

Randall Sakai and colleagues at the University of Cincinnati College of Medicine used the technique of somatic cell transfer to produce cloned mice - that is placing the nucleus of an adult cell into an enucleated donor cell. They measured various parameters of obesity and found the cloned mice were heavier than controls after 10 weeks growth. The clones were not simply larger than controls, but displayed all the characteristics of obesity - increased body fat, increased leptin levels, and raised plasma levels of insulin. Importantly, the offspring of these mice were not obese, meaning that the abnormality was not passed on through the germline.

Ian Wilmut, a key member of the team that generated the first clone, Dolly the sheep, writes an accompanying News & Views article (p. 215) discussing the work. He asks whether any cloned animals are normal, and writes that detailed observations of clones “…are important before large-scale use of the technology in medicine…” can take place.